APP 01

BOW THRUSTER
RIGHT-ANGLE DRIVE

Bevel gear specification: M10–M18, 17-4 PH H900 or 18CrNiMo7-6 with electroless nickel, spiral bevel, ratio 1:1 to 2:1, DNV GL or BV class approval, sealed housing IP67. The bow thruster right-angle bevel gearbox converts the horizontal motor shaft (mounted in the vessel’s bow void) to the vertical propeller shaft of the tunnel thruster. Motor power is 100–3,000 kW on commercial vessels; the bevel gear operates continuously during port manoeuvring at full rated power. The gearbox housing is mounted in the thruster tunnel — a permanently wet environment exposed to sea water when the vessel is underway. 17-4 PH H900 spiral bevel gears in a 316L stainless housing with double lip seals and sacrificial zinc anodes on the housing are the standard specification for bow thruster bevel gearboxes on commercial vessels. Korea Ever-Power supplies bow thruster bevel gear replacement sets for Wärtsilä, Rolls-Royce (Kamewa), Brunvoll, and Thrustmaster thruster models.

APP 02

STEERING GEAR
RAM DRIVE

Bevel gear specification: M10–M16, 17-4 PH H900 or 18CrNiMo7-6 nickel-plated, spiral bevel, ratio 1:1 to 3:1, class approved, SOLAS (Safety of Life at Sea) redundancy requirements. The vessel steering gear uses a bevel gear right-angle drive to transfer the hydraulic pump motor shaft rotation to the rudder stock. SOLAS Chapter II-1 Regulation 29 requires that all vessels above 150 GT carry steering gear capable of moving the rudder from 35° to 35° port-to-starboard in 28 seconds at maximum service speed, with a redundant power unit. The bevel gears in the steering gear must be designed to this emergency manoeuvring load, not just the normal steady-speed load. Korea Ever-Power’s marine steering gear bevel gears are designed to SOLAS emergency steering load with a safety factor of 1.5 applied to the emergency torque, and supplied with class certification for incorporation into the steering gear classification documentation.

APP 03

ANCHOR WINDLASS
& DECK WINCH

Bevel gear specification: M8–M14, 17-4 PH H900 or 316L stainless, straight or spiral bevel, ratio 1:1 to 3:1, shock service factor 2.0–2.5. Anchor windlass and deck mooring winch bevel gearboxes are subject to severe shock loads when the anchor cable suddenly takes up slack during vessel ranging in a seaway or when a mooring line snaps under tension. The bevel gear must absorb these shock loads without tooth fracture. Open or semi-open deck environments require maximum corrosion protection — 17-4 PH H900 stainless bevel gears in stainless housings with pressurised oil lubrication and positive shaft sealing are specified for windlass gearboxes on vessels operating in Arctic and tropical marine environments. Deck equipment bevel gears also experience temperature extremes — from -40°C in Arctic service to +50°C in tropical port operation — requiring the gear lubricant viscosity selection to account for both extremes in a single oil fill.

APP 04

NAVAL & PATROL
VESSEL DRIVES

Bevel gear specification: M12–M20, Nitronic 50 XM-19 or 17-4 PH H900, spiral bevel, MIL-G-17859 or DEF STAN 02-302 (Royal Navy) material certification, high shock service factor 2.5–3.5. Naval patrol vessels and offshore patrol vessels (OPVs) require bevel gears certified to military specifications for shock resistance — naval vessels must maintain propulsion after underwater explosion (UNDEx) events that impose severe multi-axis shock loads on the gearbox. Nitronic 50 (a nitrogen-strengthened austenitic stainless steel, yield strength 520 MPa, superior to 316L) is specified by several navies for deck equipment bevel gears because it combines high strength with the salt water corrosion resistance required for indefinite service without corrosion protection maintenance. Korea Ever-Power supplies naval specification bevel gears with MIL material certification and traceable heat treatment records on request.

What lubricant is correct for a marine bow thruster bevel gearbox, and how is the oil change managed when the thruster is mounted in a permanently wet tunnel?

Marine bow thruster bevel gearboxes use ISO VG 220 or VG 320 gear oil with rust inhibitor and anti-emulsification additive packages (critical for any marine gearbox oil). Synthetic PAO-based gear oil (Klüber Klübersynth GH 6-220 or equivalent) is preferred for sealed-for-long-interval service because PAO does not oxidise as rapidly as mineral oil at elevated operating temperatures, extending the service interval to 4,000–8,000 hours. Oil change in a thruster tunnel gearbox: most commercial thruster gearboxes are equipped with a dedicated oil drain pipe and fill connection routed to an accessible location in the bow void — oil change does not require drydocking or tunnel access when this system is correctly installed. If the vessel does not have these connections, oil change must be performed at drydocking with the tunnel dewatered. Korea Ever-Power recommends quarterly oil sampling and analysis for bow thruster gearboxes on vessels operating in warm tropical waters above 30°C — the elevated oil temperature significantly accelerates oxidation and increases water contamination risk from seal degradation. Discard and replace oil immediately if water content exceeds 0.5% by volume (Karl Fischer titration on oil sample).

Why is 17-4 PH preferred over 316L stainless steel for heavy-duty marine bevel gears?

17-4 PH (AISI 630, UNS S17400) and 316L (UNS S31603) are both stainless steels with good marine corrosion resistance, but they differ fundamentally in strength and hardenability: 316L in the annealed condition has yield strength of 170–210 MPa and cannot be hardened beyond approximately HB 200 — providing very limited bending fatigue strength for gear tooth roots. 17-4 PH in the H900 precipitation-hardened condition achieves yield strength of 1,170 MPa and HRC 38–43 — approximately four times the strength of annealed 316L, with bending fatigue strength sufficient for medium-to-heavy marine bevel gear applications. The trade-off: 17-4 PH has slightly lower crevice corrosion resistance than 316L in stagnant seawater (because it is a martensitic-type PH stainless rather than austenitic), but in a properly lubricated enclosed gear housing with no stagnant water contact this is not a relevant distinction. For marine bevel gears above 5 kW transmitted power: 17-4 PH H900 is the correct choice. For small marine bevel gears below 5 kW in permanently wet or bilge environments where load capacity is not the constraint: 316L annealed is acceptable and lower in cost.

What is the lead time for replacement spiral bevel gears for a bow thruster or steering gear at drydock?

Lead time for marine spiral bevel gear replacement sets from Korea Ever-Power depends on the gear size and certification requirement: (1) Standard marine bevel gears M8–M12, 17-4 PH, no class certification: 20–30 days from drawing confirmation. (2) Marine bevel gears M12–M18, 17-4 PH or 18CrNiMo7-6, with DNV GL or BV material certification: 35–50 days — the additional lead time allows for class surveyor review of the material mill certificate and heat treatment records before shipment. (3) Naval specification bevel gears with MIL material certification: 45–65 days from drawing and specification confirmation. For drydocking projects with a fixed vessel arrival date at the repair yard, Korea Ever-Power recommends ordering replacement marine bevel gears at least 60–70 days before the planned drydock date to ensure gear availability before the vessel arrives. Emergency orders for critical propulsion or steering gear bevel gear failures at sea can be expedited — contact Korea Ever-Power’s emergency response team with the vessel name, IMO number, gear geometry, and the port of repair for the fastest available supply route including air freight to the repair port.

Spur Gears

M1–M20 · 17-4 PH · 316L marine

Helical Gears

Marine gearbox · propulsion · 18CrNiMo7-6

Engrenages coniques

17-4 PH · marine · thruster · steering

Worm Gears

Self-locking · winch brake · valve drive

Ring Gears

Stainless · slewing · marine planetary

Planetary Gears

Compact · thruster hub · winch drive

Plastic Gears

UHMWPE · PEEK · bilge · instrument